Blender 2.83, Cycles, can't get pointiness to work
As mentioned in the comments, on a cube with no curvature,or any type of bevel, you will see no result from  the pointiness output of the geometry node.
Pointiness as defined in the manual:

An approximation of the curvature of the mesh per vertex. Lighter values indicate convex angles, darker values indicate concave angles. It allows you to do effects like dirt maps and wear-off effects.

You can see this clearly in the following example:
All objects have the same basic node setup including the default cube on the left.

Click to enlarge
The node seteup used: